I had powdery mildew - started on Jan 11th THIS YEAR!
The reason I know the exact date is because that was the date somebody gave me four "free" clones. He told me there was some mildew on them and that he sprayed them. But of course I was clueless, as I had never experienced mildew before. Within ten days or so, the mildew spread from my cloning box to my flowering room. I remember it looking like there was almost snow on the leaves one sunday morning. I went down to the local Loew's store and bought some all purpose spray mix (Ortho) and started sprying. The spray had a nasty smell to it. A week later, my grow store sold me a bottle of spray which quite organic and very gentle on the plants, and I believe it worked much better than the Ortho stuff I bought. But it would come back every few days even with full ventilation 24 hrs a day.

I then heard about burning sulfur. That it would take care of it once and for all. The grow shop wanted over $100 for a complete kit. I wanted it, but that's a lot of money! So went to a nursery wholesale supplier and asked for a bag of sulfur. "Sulfur pellets?" was the reply, and I said yes. I now had 50 lbs of sulfur pellets. Next stop was the local Goodwill store where I purchased a single electric burner that works on 120V. It's the kind you would typlically use in an office lunchroom somewhere so you could boil a kettle of water. They had a nice one for $3. Then I bought a smaller iron skillet for another $4. When I got home the I turned off all fans (no lights on) and set up my little burner with the frying pan on it and filled the pan 3/4 full of pellets. Withing about 3 or 4 minutes the pellets melted, and some smoke was generated. It took me a bit of fiddling to set the burner temperature so that the stuff won't catch on fire (as I was told it could), but yet make enough smoke to fill the room. For my particular burner I just marked the setting with felt pen for my own information. I then set a small fan behind the "smoking pan" to distribute the smoke.

I did this twice in two weeks for four hours at a time, and my problems have been completely eliminated!

wallhofen